1. Field of the Invention
The present invention relates to a magnetoresistance effect film for reading the magnetic field intensity of a magnetic recording medium or the like as a signal and, in particular, to a magnetoresistance effect film which is capable of reading a small magnetic field change as a greater electrical resistance change signal, and further relates to a magnetoresistance effect type head using such a magnetoresistance effect film. They are mainly incorporated in, for example, hard disk drives so as to be used.
2. Description of the Prior Art
Recently, following the high densification of hard disks, highly-sensitive heads with high outputs have been demanded. In response to these demands, spin valve heads have been developed.
The spin valve head has a structure wherein two ferromagnetic layers are formed via a non-magnetic metal layer, and an antiferromagnetic layer is disposed so as to abut one of the ferromagnetic layers. The ferromagnetic layer abutting the antiferromagnetic layer is in exchange coupling to the antiferromagnetic layer so that the magnetization of the ferromagnetic layer is fixed (pinned) in one direction. The magnetization of the other ferromagnetic layer is freely rotated following the change of the external magnetic field. In the spin valve, the MR change is realized by a difference in relative angles of spins between the two ferromagnetic layers. Therefore, the exchange coupling between the antiferromagnetic layer and the ferromagnetic layer abutting thereto can be said to be the substance of the spin valve.
As a material of an antiferromagnetic layer used in the spin valve, FeMn, NiMn, PtMn or the like has been well known.
When FeMn is used as the antiferromagnetic layer, the exchange coupling is generated relative to the ferromagnetic layer immediately after the formation of a film. Thus, a heat treatment for generating the exchange coupling is not required after the film formation. However, there is raised a limitation in order of the film formation that the antiferromagnetic layer should be formed after the formation of the ferromagnetic layer. Further, when FeMn is used, there is a problem that a blocking temperature is low, i.e. about 150 to 170xc2x0 C. The blocking temperature is a temperature at which the exchange coupling pinning a magnetic layer is lost.
On the other hand, when NiMn or PtMn is used as the antiferromagnetic layer, the blocking temperature is high, i.e. no lower than 300xc2x0 C., and further, there is no limitation in order of the formation of the antiferromagnetic layer and the ferromagnetic layer. However, for generating the exchange coupling between the antiferromagnetic layer and the ferromagnetic layer, a heat treatment is required in the magnetic field after stacking both layers. This is because, for NiMn or PtMn to exhibit the antiferromagnetism, a CuAuxe2x80x94I type regular crystal structure having a face centered tetragonal (FCT) structure needs to be formed. The heat treatment in the magnetic field is normally carried out under a temperature condition of 250 to 350xc2x0 C. The degree of exchange coupling tends to be increased as the temperature is raised. However, if the heat treatment at high temperatures is applied to the spin valve film, a magnetoresistance change ratio (MR ratio) being an important film characteristic of the spin valve film is lowered. Therefore, it is desired that the heat treatment for generating the exchange coupling between the antiferromagnetic layer and the ferromagnetic layer abutting thereto be carried out at a temperature as low as possible which can achieve the exchange coupling to a given level.
The present invention has been made under these circumstances and has an object to provide a magnetoresistance effect film and a magnetoresistance effect type head which, when NiMn or PtMn is used as an antiferromagnetic layer, can lower the regulating temperature of the antiferromagnetic layer to generate the exchange coupling at a heat treatment temperature as low as possible (for example, no higher than 250xc2x0 C.) so that a spin valve film characteristic (for example, MR ratio) is not adversely affected.
As the prior art literature relevant to the present invention, there are U.S. Pat. No. 5,608,593 and JP-A-9-63021.
U.S. Pat. No. 5,608,593 discloses a spin valve film having a structure wherein a buffer layer made of Cu or NiCr, an antiferromagnetic layer made of FeMn, NiMn or NiCoO and a ferromagnetic layer pinned by the antiferromagnetic layer are formed in the order named on an underlayer formed on a substrate. The buffer layer is described to have an adequate microstructure and functions of promoting a phase of the antiferromagnetic layer and preventing mutual diffusion between the underlayer and the antiferromagnetic layer. However, only by a simple combination of the buffer layer made of Cu and the antiferromagnetic layer made of NiMn, the foregoing object of the present invention can not be accomplished to a sufficient level. Specifically, there is a problem that a temperature for regulating crystals is not lowered so much.
On the other hand, JP-A-9-63021 discloses a spin valve film having a structure wherein a film obtained by stacking Ta and NiFe is used as an underlayer, and an antiferromagnetic layer made of NiMn and a ferromagnetic layer pinned by the antiferromagnetic layer are formed in the order named on the underlayer. It is described that Ta of the underlayer is used for smoothing the surface, while NiFe of the underlayer is used for allowing NiMn to easily form an FCT structure. However, if the underlayer made of NiFe is used, there is raised a disadvantage that this ferromagnetic body exerts a magnetically bad influence on the spin valve film.
For solving the foregoing problems, according to one aspect of the present invention, there is provided a spin valve type magnetoresistance effect film comprising a multilayered film including a non-magnetic metal layer, a ferromagnetic layer formed on one surface of the non-magnetic metal layer, a soft magnetic layer formed on the other surface of the non-magnetic metal layer, an antiferromagnetic layer which is formed on a surface of the ferromagnetic layer remote from a surface thereof abutting the non-magnetic metal layer so as to pin a direction of magnetization of the ferromagnetic layer, and an antiferromagnetization promote layer formed on a surface of the antiferromagnetic layer remote from a surface thereof abutting the ferromagnetic layer, wherein the antiferromagnetic layer is made of a compound containing Mn and having a CuAuxe2x80x94I type regular crystal structure, the antiferromagnetic layer has a characteristic requiring a heat treatment for generating exchange coupling relative to the ferromagnetic layer, and the antiferromagnetic layer after the heat treatment is oriented on a (111) crystal orientation surface, and wherein a ratio Lp/La of a lattice constant Lp in a closest packed surface of the antiferromagnetization promote layer relative to a lattice constant La in the (111) crystal orientation surface of the antiferromagnetic layer is in the range of 0.9 to 1.1.
It is preferable that the antiferromagnetic layer oriented on the (111) crystal orientation surface is made of PtMn or an alloy containing PtMn at least no less than 80 at %, and that the antiferromagnetization promote layer is made of at least one selected from Ir, Pd, Pt, Rh, Ru, Re, Os, Al, Cu, Au and Ag.
It is preferable that the antiferromagnetization promote layer is made of at least one selected from Pd, Pt, Rh and Re.
It is preferable that the antiferromagnetic layer oriented on the (111) crystal orientation surface is made of NiMn or an alloy containing NiMn at least no less than 80 at %, and that the antiferromagnetization promote layer is made of at least one selected from Ir, Pd, Pt, Rh, Ru, Re and Os.
It is preferable that the antiferromagnetization promote layer is made of at least one selected from Ir, Pd and Rh.
It is preferable that a thickness of the antiferromagnetization promote layer is 0.1 to 10 nm.
It is preferable that a laminate structure is formed by the antiferromagnetization promote layer, the antiferromagnetic layer, the ferromagnetic layer, the non-magnetic metal layer and the soft magnetic layer which are stacked in the order named on a substrate directly or via an underlayer.
It is preferable that a laminate structure is formed by the antiferromagnetization promote layer, the antiferromagnetic layer, the ferromagnetic layer, the non-magnetic metal layer and the soft magnetic layer which are stacked in the order named on an underlayer formed on a substrate, and that the underlayer is made of at least one selected from Ta, Hf, Zr and Ti.
According to another aspect of the present invention, there is provided a magnetoresistance effect type head comprising a magnetoresistance effect film, conductive films and electrode portions, wherein the conductive films are conductively connected to the magnetoresistance effect film through the electrode portions, wherein the magnetoresistance effect film is a spin valve type magnetoresistance effect film which comprises a multilayered film including a non-magnetic metal layer, a ferromagnetic layer formed on one surface of the non-magnetic metal layer, a soft magnetic layer formed on the other surface of the non-magnetic metal layer, an antiferromagnetic layer which is formed on a surface of the ferromagnetic layer remote from a surface thereof abutting the non-magnetic metal layer so as to pin a direction of magnetization of the ferromagnetic layer, and an antiferromagnetization promote layer formed on a surface of the antiferromagnetic layer remote from a surface thereof abutting the ferromagnetic layer, wherein the antiferromagnetic layer is made of a compound containing Mn and having a CuAuxe2x80x94I type regular crystal structure, the antiferromagnetic layer has a characteristic requiring a heat treatment for generating exchange coupling relative to the ferromagnetic layer, and the antiferromagnetic layer after the heat treatment is oriented on a (111) crystal orientation surface, and wherein a ratio Lp/La of a lattice constant Lp in a closest packed surface of the antiferromagnetization promote layer relative to a lattice constant La in the (111) crystal orientation surface of the antiferromagnetic layer is in the range of 0.9 to 1.1.
It is preferable that the antiferromagnetic layer oriented on the (111) crystal orientation surface is made of PtMn or an alloy containing PtMn at least no less than 80 at %, and that the antiferromagnetization promote layer is made of at least one selected from Ir, Pd, Pt, Rh, Ru, Re, Os, Al, Cu, Au and Ag.
It is preferable that the antiferromagnetization promote layer is made of at least one selected from Pd, Pt, Rh and Re.
It is preferable that the antiferromagnetic layer oriented on the (111) crystal orientation surface is made of NiMn or an alloy containing NiMn at least no less than 80 at %, and that the antiferromagnetization promote layer is made of at least one selected from Ir, Pd, Pt, Rh, Ru, Re and Os.
It is preferable that the antiferromagnetization promote layer is made of at least one selected from Ir, Pd and Rh.
It is preferable that a thickness of the antiferromagnetization promote layer is 0.1 to 10 nm.
It is preferable that the magnetoresistance effect film comprises a laminate structure formed by the antiferromagnetization promote layer, the antiferromagnetic layer, the ferromagnetic layer, the non-magnetic metal layer and the soft magnetic layer which are stacked in the order named on a substrate directly or via an underlayer.
It is preferable that the magnetoresistance effect film comprises a laminate structure formed by the antiferromagnetization promote layer, the antiferromagnetic layer, the ferromagnetic layer, the non-magnetic metal layer and the soft magnetic layer which are stacked in the order named on an underlayer formed on a substrate, and that the under layer is made of at least one selected from Ta, Hf, Zr and Ti.